The present invention relates to improvements in methods and apparatus for installing a replacement pipeline section inside an existing underground conduit such as a pipeline section in need of repair or replacement. The present invention is particularly concerned with the installation of a replacement pipeline section within building sewers intersecting sewer mains, within other lateral pipelines, intersecting main pipelines, within pipeline sections that may include curves and abrupt bends, and within still other pipeline sections which are intersected by building sewers, the connections of laterals which would be difficult to locate after a new pipeline section is installed within the existing pipeline section.
Various processes and apparatuses have Open suggested for repairing underground pipelines such as sewer lines and the like, with the existing pipeline remaining in place underground, by installing within the existing pipe a flexible membrane or liner of plastic or by inserting into the existing pipe a new plastic pipe.
In one known process, pipes are lined with a flexible plastic Such as polyethylene. According to this process the liner is installed through insertion pits at intervals along the pipeline, making the process expensive.
According to another process, shown in, for example, U.S. Pat. Nos. 3,927,164 and 4,064,211 a flexible tube is turned inside out as it is inflated and blown into a pipeline section from one end of the section. This process is expensive because it requires special equipment, extensive heating and expensive materials.
The above mentioned processes and most others use a flexible or semi-flexible liner which is not capable of withstanding any appreciable external hydrostatic or earth pressures. Thus the existing pipe may not be properly repaired since if any part of it is broken away, the liner can possibly collapse from external pressure of any magnitude, such as pressures, for example, which exceed about 4 pounds per square inch.
Both Thomas et al U.S. Pat. No. 4,394,202 and Harper et al U.S. Pat. No. 2,794,758 also disclose processes of inserting flexible tubing into an existing pipeline as a lining membrane for that pipeline. Thomas discloses a method of attaching the flexible tubing to the existing pipeline using an expandable short section of adhesive-coated rigid plastic. Both the Thomas and Harper processes have the same drawbacks as previously mentioned with respect to other prior processes using flexible membrane material in that they lack the necessary hoop strength to withstand external earth and hydraulic pressures.
Others have suggested inserting a rigid tube inside the existing pipeline in need of repair. For example, in the published British application No. 2,084,686 an oversized round rigid plastic tube is flattened or otherwise reduced at the job site and then inserted cold and rigid into the existing pipeline through a large excavation at a manhole. After insertion, the plastic tube is expanded using heat and internal pressure. The plastic tube is expanded against the existing pipe.
According to British Patent No. 1,580,438, an existing underground pipe is lined with a plastic liner tube made of a plastic material such as polyethylene or polypropylene having a plastic memory. The liner tube is manufactured in an out-of-round "U" shape to fit inside the existing pipe, then inserted in its out-of-round shape into the existing pipe, and then expanded against the existing pipe under heat and pressure to a round condition.
The published EPC Patent Application No. 0,000,576 suggests inserting a semi-rigid plastic tube insert inside an existing pipe. The semi-rigid plastic tube has sufficient hoop strength to withstand all or at least part of the external pressures that may be imposed upon it.